1. Field of the Invention
The present invention relates to a method and base station system for configuring a radio interface between a mobile station and a base station of a time-division multiplex mobile radio telephone system for a packet data transmission data transmission.
2. Description of the Prior Art
Connection-oriented concepts and concepts on the basis of logical connections can be recoursed for the transmission of data between two pieces of communication terminal equipment. Given connection-oriented data transmissions, physical resources between the two pieces of communication terminal equipment must be offered during the entire time of the data transmission.
A permanent offering of physical resources is not necessary given data transmission via logical connections. An example of such a data transmission is packet-data transmission. Here, a logical connection between the two pieces of communication terminal equipment exists during the duration of the entire data transmission. However, physical resources are offered only during the actual transmission times of the data packets. This method is based on the fact that the data are communicated in short data packets between which longer pauses can occur. The physical resources are available for other logical connections in the pauses between the data packets. Physical resources are saved with reference to a logical connection.
The packet data transmission method disclosed by German Letters Patent DE 44 02 930 A1 is particularly suitable for communication systems having physical limited resources. The physical resources in the frequency domainxe2x80x94the number of frequency channels and time slotsxe2x80x94are limited and must be rationally utilized in, for example, mobile radio telephone systems such as the GSM mobile radio telephone system (global system for mobile communications).
The GSM mobile radio telephone system is an example of a time-division multiplex mobile radio telephone system, whereby time slots within a frequency channel can be divided onto different communication terminal equipment. The network-side radio station of a mobile radio telephone network is a base station that communicates with mobile stations via a radio interface. The transmission from a mobile station to the base station is referred to as upstream direction; the transmission from the base station to a mobile station is referred as downstream direction. A channel that is reserved for the packet-data transmission is formed by at least one time slot per time-division multiplex frame. Further, the carrier frequency and, potentially, a frequency skip sequence identify the channel.
The GSM mobile radio telephone system was originally designed for the transmission of voice, whereby a channel was reserved for the constant information transmission between mobile station and base station. In packet data transmission, however, a common channel is used for packet-data transmission for a plurality of mobile stations. Signaling information, for which a time slot is provided within the channel at cyclical intervals, is transmitted in addition to the packet data.
What the distinction in the logical and physical connections yields is that a logical connection in fact exists for a mobile station but no packet data is transmitted over a certain time span. Measurements of the base station with respect to the transmission conditions of the mobile station, however, are not possible as long as no transmission is occurring from the mobile station to the base station. Previously calculated values become invalid and must be re-identified given a renewed allocation of physical channels or, respectively, the base station must assure that the transmission conditions are set such that a protected transmission is possible in any case. This latter situation, for example, leads to an elevated or even maximum transmission power setting.
The present invention, therefore, is based on the object of specifying a method and a system with improved configuration of an air interface for packet data transmission.
Pursuant to the present invention, the mobile stations are identified with abbreviated identifiers. In the method for configuring the radio interface, time slots for signaling for the upstream direction are allocated to the mobile stations. The allocation of one or more time slots for signaling for the upstream direction occurs according to a prescribable sequence, wherein the allocation occurs with indicator messages that contain abbreviated identifiers and time slot designations. The allocation is thus independent of a sequence of the packet data transmission from or to the mobile station.
As a result of a flexible allocation of a time slot for signaling even, a for mobile stations to which no physical channel is allocated at the moment, the base station can implement a continuous measurement to the radio interface. Given re-assumption of the packet data transmission, valid measured values are thus immediately available for configuring the radio interface.
According to a further advantageous development, the abbreviated identifiers of the mobile stations are selected in addition to their identifications within the mobile radio telephone system for the packet data transmission. The abbreviated identifiers enable an improved resource utilization between the network and the mobile stations via the radio interface to since they are independent of addresses for the mobile stations known in the network, and the signaling is flexibly designed according to individual requirements independently of the packet data transmission.
In a further development of the method for configuring the radio interface, configuration data with respect to the radio interface for a plurality of mobile stations are combined and transmitted in a time slot for signaling. Such a signaling is of significance for the downstream direction since information for configuring the radio interface for the mobile station, for example the values related to the transmission power setting or, respectively, the timing advance for the transmission time, is contained in it. Since only a few particulars are required per mobile station, a combining of the configuration data in one message saves transmission capacity that is now available for neighboring cell measurements or for some other kind of signaling information.
The configuration data for a mobile station can be transmitted together with the configuration data for other mobile stations in a single time slot for signaling in a downstream direction, advantageously repeated or provided with a coating or error recognition in this case, or in a plurality of non-successive time slots for signaling. In the latter instance, the nesting provides protection against error. Which time slots are combined to form such a signaling block can be set. Given such a utilization of, for example, a second time slot for signaling, the intervening time slots can be utilized for neighboring cell measurements.
The portion of time slots for the neighboring cell measurements can be increased further when less configuration data (for example, only the timing advance) is transmitted or, respectively, when only few mobile stations are to be covered. A cyclical adaptation of the sequence of the combining thereby can be provided. Such an adaptation creates an improved matching of the signaling outlay to the actual requirements of the mobile stations for a packet data transmission. The closed control circuit for the timing advance can be achieved according to the present invention, since mobile stations have time slots allocated to them for signaling in the upstream direction and signaling blocks for the mobile stations arrive in downstream direction with a short delay time. Only the mobile station and the base station advantageously participate in this control circuit. Since, differing from packet data transmission, no concrete allocation between a mobile station and a data block (which is usually implemented in a base station controller) is needed for this signaling, the base station can undertake the setting of the timing advance by itself. Signaling outlay between the base station and the base station controller is thereby eliminated.
According to a further development of the present invention, the configuration for the timing advance occurs independent of the transmission power setting. The timing advance is defined according to a closed control circuit between mobile station and base station, wherein a longer cycle can be provided between two determinations on the basis of a suitable selection of the time slots for signaling. The timing advance has to be identified only at a spacing of a few seconds in view of the slow movement of the mobile station relative to the signal propagation speed.
In the determination of the transmission power setting of the base station, the transmission power is advantageously directed onto the mobile station with the poorest transmission correction on the common channel. Open or closed control circuits can be established for this purpose independently of a determination of the timing advance. Given great differences between the transmission power required for individual mobile stations and given a presence of a plurality of common channels, it is advantageous to allocate the mobile stations to the channels according to the required transmission power.
Advantageously, the packet data transmission in each transmission direction, i.e. in upstream direction and downstream direction, occurs independently of one another. Consequently, a mobile station can transmit data in upstream direction or receive data from the network in downstream direction. A packet data transmission in both directions also can be provided for a mobile station. The separation into upstream and downstream direction enables a great flexibility in the utilization of the radio-oriented resources and, of course, in the design of the mobile station as well, which potentially only transmits or receives.
Advantageously, a closed message is communicated to the base station from a mobile station within a time slot for signaling. This closed message contains, for example, reception values of the mobile station for signals of the base station, as a result whereof an immediate transmission power setting of the base station is possible given a packet data transmission in downstream direction. In that one closed message is communication per time slot, the time until the reception level of the mobile station is present at the base station and the time for the configuration of the radio interface are shortened. The base station determines the timing advance or, respectively, the reception level of the base stations with reference to the respective mobile station from transmissions for signaling in upstream direction.
The specific value or values or, respectively, control values for the timing advance and the transmission power are communicated to the mobile station in downstream direction, whereupon this also can undertake the necessary settings for configuration of the radio interface.
The configuring is accelerated further when the determination of the timing advance and/or of the reception level of the base station is additionally undertaken from the time slots for the packet data transmission. The allocation of abbreviated identifiers to mobile stations can also influence the setting time of the configuration. The setting time is shortened, for example, when a plurality of abbreviated identifiers are allocated to a mobile station. It is likewise possible to keep the delay times short on the basis of a corresponding selection of specific abbreviated identifiers at the end of a macro frame. The limitation of the number of abbreviated identifiers leads to a faster re-employment of a time slot for signaling for a mobile station and to a shortening of the delay time. The plurality of abbreviated identifiers is advantageously set according to the transmission conditions and the number of mobile stations provided for the packet data service.
When a plurality of time slots for signaling are combined in downstream direction to form a signaling block, then the signaling advantageously occurs simultaneously for a plurality of mobile stations. The signaling in downstream direction, however, can likewise occur within packet data so that, for example, the transmission power setting can be continuously adapted without utilizing time slots for signaling and additional time slots are available for neighboring cell measurement.
The signaling outlay also can be lowered by the selection of specific transmission block types. When normal transmission blocks (normal bursts) are employed by contrast to what are referred to as access bursts, an identification of reception power is possible by averaging over a greater plurality of bits, as a result whereof the measuring precision is increased or, respectively, a lower number of repeated measure values is required for setting the transmission power. Such longer transmission blocks are advantageously employed for setting the transmission power when valid values for the timing advance are already present.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawing.